Toner and Method of Producing Toner

This application is a Continuation of International Patent Application No. PCT/JP2023/045961, filed Dec. 21, 2023, which claims the benefit of Japanese Patent Application No. 2022-207914, filed Dec. 26, 2022, Japanese Patent Application No. 2023-207601, filed Dec. 8, 2023, and Japanese Patent Application No. 2023-210365, filed Dec. 13, 2023, all of which are hereby incorporated by reference herein in their entirety.

The present disclosure relates to a toner used in an electrophotographic system, an electrostatic recording system, an electrostatic printing system, and a toner jet system and a method of producing a toner.

In recent years, electrophotographic devices such as full-color printers and full-color copying machines have been increasingly required to provide additional value such as high productivity, high image quality, and high stability.

In order to achieve high productivity, it is important to melt a toner more quickly during a fixing step. Specifically, when the main component of a binder resin of the toner is a crystalline resin having sharp melting properties, it is possible to achieve excellent low-temperature fixability as compared to a toner whose main component is an amorphous resin.

For example, Japanese Patent Laid-Open No. 2014-130243 proposes a toner that achieves both low-temperature fixability and heat-resistant storability by using an acrylate-based resin having crystallinity in the side chain. However, it has been found that a toner using a crystalline resin having low-temperature fixability exhibits low strength at normal temperature and the fixed image is vulnerable to rubbing and scratching.

Thus, Japanese Patent Laid-Open No. 2014-142632 proposes a toner that enables low-temperature fixing by using a binder resin in which a crystalline vinyl resin matrix and an amorphous resin domain are used in combination, and produces images that are resistant to external forces such as rubbing and scratching due to its domain structure.

On the other hand, the performance required for electrophotographic devices has been increasing year by year, and it is required to stably obtain printed outputs with high image quality even when outputting at a high speed and in a large amount over a long period of time under various environments. In addition, the robustness of the printed outputs has also become important, and they are required to have resistance to abrasion and scratches and heat resistance. In addition, there is also a demand for achieving image glossiness and reducing image density non-uniformity on fixing media with significant unevenness such as rough paper.

According to studies performed by the inventors, the toner described in Japanese Patent Laid-Open No. 2014-142632 is insufficient to meet the currently required level of image robustness, and there is a strong demand for improvement, particularly in the scratch resistance of images printed on smooth media such as coated paper.

At least one aspect of the present disclosure provides a toner that exhibits excellent low-temperature fixability and excellent resistance to scratches on an image printed on smooth media such as coated paper, and can achieve image glossiness and reduce image density non-uniformity on fixing media with significant unevenness. In addition, at least one aspect of the present disclosure provides a method of producing the toner.

At least one aspect of the present disclosure relates to a toner comprising a toner particle comprising a binder resin and a wax, wherein the binder resin comprises a crystalline resin, the content of the crystalline resin based on the mass of the toner particle is 30.0 to 95.0 mass %, in viscoelastic measurement of the toner, when a storage elastic modulus of the toner at a temperature T (° C.) is G′(T), in a graph in which a horizontal axis represents the temperature T, and a vertical axis represents a value d(log G′(T))/dT obtained by differentiating Log G′(T) with respect to the temperature T, the local minimum value is observed in a range of 50.0 to 70.0° C., and when a temperature at which the local minimum value is reached is defined as a temperature T1 (° C.), d(log G′(T1))/dT is −2.00 to −0.20, d(log G′(T1+3))/dT≤0, d(log G′(T1+3))/dT−d(log G′(T1))/dT is 0.15 to 1.90, G′(T1) is 5.0×10to 2.0×10Pa, and G′(T1+30) is 1.0×10to 5.0×10Pa.

At least one aspect of the present disclosure relates to a method of producing the above-mentioned toner, the method comprising: a melt-kneading step in which a mixture comprising the crystalline resin and the wax is melt-kneaded; and an annealing step in which the melt-kneaded product obtained in the melt-kneading step is held at a temperature at least 5° C. higher than the melting point of the crystalline resin.

Features of the present disclosure will become apparent from the following description of embodiments.

In the present disclosure, “from XX to YY” or “XX to YY” indicating a numerical range means a numerical range including a lower limit and an upper limit that are end points unless otherwise specified.

The term (meth)acrylic acid ester refers to an acrylic acid ester and/or methacrylic acid ester.

When the numerical ranges are expressed in stages, the upper limits and lower limits of the numerical ranges can be arbitrarily combined.

The term “monomer unit” refers to a reacted form of a monomer substance in a polymer. For example, one unit is one carbon-carbon bond segment in the main chain of a polymer formed by polymerizing vinyl-based monomers. The vinyl-based monomer can be represented by the following formula (Z).

In the formula (Z), Rrepresents a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group), and Rrepresents an optional substituent.

The crystalline resin is a resin that exhibits a clear endothermic peak in differential scanning calorimeter (DSC) measurement.

Hereinafter, a toner of the present disclosure will be described in detail.

The present disclosure relates to a toner comprising a toner particle comprising a binder resin and a wax, wherein the binder resin comprises a crystalline resin, the content of the crystalline resin based on the mass of the toner particle is 30.0 to 95.0 mass %, in viscoelastic measurement of the toner, when a storage elastic modulus of the toner at a temperature T (° C.) is G′(T), in a graph in which a horizontal axis represents the temperature T, and a vertical axis represents a value d(log G′(T))/dT obtained by differentiating Log G′(T) with respect to the temperature T, the local minimum value is observed in a range of 50.0 to 70.0° C., and when a temperature at which the local minimum value is reached is defined as a temperature T1 (° C.), d(log G′(T1))/dT is −2.00 to −0.20, d(log G′(T1+3))/dT≤0, d(log G′(T1+3))/dT−d(log G′(T1))/dT is 0.15 to 1.90, G′(T1) is 5.0×10to 2.0×10Pa, and G′(T1+30) is 1.0×10to 5.0×10Pa.

The inventors conducted extensive studies, and as a result, found that, in a toner containing a crystalline resin, when the viscoelasticity of the toner is controlled to be within a specific range, the toner exhibits excellent low-temperature fixability and scratch resistance for images printed on smooth media.

The inventors speculate the reason why the above problem has been solved is as follows.

The crystalline resin used in the toner has a smaller internal cohesive force than the amorphous resin, and is easily destroyed when subjected to external forces such as scratching or rubbing, resulting in low image robustness. In Japanese Patent Laid-Open No. 2014-142632, a sea-island structure is formed using a crystalline resin and an amorphous resin in combination, and the image intensity can be increased to a certain extent. However, since the sea part, which is a continuous layer, is formed of the crystalline resin with a low internal cohesive force, significant improvements in the robustness of the image have not been possible.

On the other hand, the toner of the present disclosure has the following features.

In viscoelastic measurement of the toner, when a storage elastic modulus of the toner at T (° C.) is defined as G′(T), a graph in which a horizontal axis represents the temperature T, and a vertical axis represents a value d(log G′(T))/dT obtained by differentiating Log G′(T) with respect to the temperature T is obtained:

In a graph in which a horizontal axis represents temperature T and a vertical axis represents d(log G′(T))/dT, a local minimum value is observed at a temperature T1 (° C.) in a range of 50 to 70° C., and when d(log G′(T1))/dT is −2.00 to −0.20, this indicates that the storage elastic modulus decreases suddenly in a range of 50 to 70° C. Here, log G′(T1) indicates Log G′(T) at the temperature T1. log G′(T1+3) indicates Log G′(T) at the temperature T1+3° C.

In addition, when d(log G′(T1+3))/dT≤0, and d(log G′(T1+3))/dT−d(log G′(T1))/dT is 0.15 to 1.90, this indicates that the degree of decrease in storage elastic modulus at T1+3° C. is significantly smaller than the degree of sudden decrease in the storage elastic modulus at T1° C.

A feature that the degree of decrease in viscoelasticity of the toner differs greatly despite a small temperature difference such as 3° C. is not exhibited by conventional toners. In addition, according to studies performed by the inventors, such a feature is not exhibited unless a wax is present, and thus it is speculated that the toner according to the present disclosure has a structure different from that of conventional toners.

Specifically, the inventors speculate that the toner of the present disclosure has a structure in which a discontinuous phase of a crystalline resin alone is dispersed in a continuous phase of a eutectic of a crystalline resin and a wax. If such a structure is used, the crystalline resin in the discontinuous phase melts when the melting point of the crystalline resin is exceeded, and thus the storage elastic modulus decreases suddenly. However, once the discontinuous phase of the crystalline resin has completely melted, the viscoelasticity of the entire toner is dominated by the viscoelasticity of the eutectic of the crystalline resin in the continuous phase and the wax, which can explain why the decrease in viscoelasticity suddenly becomes small.

Assuming that images formed with the toner also have a similar structure, it is thought that, in addition to the continuous phase with an increased internal cohesive force due to the eutectic of the crystalline resin and the wax, the crystalline resin phase existing as the discontinuous phase exhibits a filler effect, and thus the image intensity can dramatically increase.

In the toner of the present disclosure, in a graph in which a horizontal axis represents the temperature T and a vertical axis represents d(log G′(T))/dT, a local minimum value is observed in a range of 50.0 to 70.0° C. The temperature at which the local minimum value is reached is defined as a temperature T1 (° C.). When the local minimum value is higher than 70.0° C., the low-temperature fixability is likely to decrease.

In order to achieve both the low-temperature fixability and storability, it is preferably in a range of 55.0 to 65.0° C., and more preferably in a range of 57.0 to 65.0° C. The temperature T1 can be controlled, for example, by changing the melting point of the crystalline resin. In addition, the temperature T1 can also be controlled by changing the glass transition point of the amorphous resin.

In addition, in the toner, in a graph in which a horizontal axis represents the temperature T and a vertical axis represents d(log G′(T))/dT, d(log G′(T1))/dT is −2.00 to −0.20. d(log G′(T1))/dT is preferably −2.00 to −0.30, more preferably −2.00 to −0.40, and still more preferably −1.70 to −0.40.

When d(log G′(T1))/dT is a value larger than −0.20, since the degree of decrease in storage elastic modulus is small, the sharp melting properties of the toner deteriorate and the low-temperature fixability decreases. Making d(log G′(T1))/dT smaller than −2.00 is a way to further improve the sharp melting properties, but it is currently difficult to perform production in the presence of other raw materials such as a colorant and an external additive contained in the toner.

In the toner of the present disclosure, in a graph in which a horizontal axis represents the temperature T and a vertical axis represents d(log G′(T))/dT, d(log G′(T1+3))/dT≤0, and d(log G′(T1+3))/dT−d(log G′(T1))/dT is 0.15 to 1.90.

When d(log G′(T1+3))/dT>0, since the storage elastic modulus increases as the temperature increases, the low-temperature fixability decreases. d(log G′(T1+3))/dT is preferably −0.50 to −0.03.

d(log G′(T1+3))/dT−d(log G′(T1))/dT indicates the difference in the degree of decrease in storage elastic modulus at the temperature T1 at which a local minimum value is reached and T1+3° C. d(log G′(T1+3))/dT−d(log G′(T1))/dT is preferably 0.20 to 1.90, more preferably 0.25 to 1.90, still more preferably 0.30 to 1.90, and yet more preferably 0.30 to 1.60.

When d(log G′(T1+3))/dT−d(log G′(T1))/dT is less than 0.15, this indicates that the difference in the degree of decrease of the storage elastic modulus is small, suggesting that the crystalline resin is also present in a continuous phase, and the scratch resistance of the formed image decreases.

Regarding the means for controlling d(log G′(T1))/dT, d(log G′(T1))/dT can be increased by increasing the content of the crystalline resin. When a crystalline vinyl resin is used as the crystalline resin, d(log G′(T1))/dT can be increased by increasing the content of the first monomer unit. In addition, d(log G′(T1))/dT can be decreased by decreasing the content of the crystalline resin. When a crystalline vinyl resin is used as the crystalline resin, d(log G′(T1))/dT can be decreased by decreasing the content of the first monomer unit. In addition, when an amorphous resin is used in combination as the binder resin, d(log G′(T1))/dT can also be controlled by changing the difference |Tc−Tg| between the melting point of the crystalline resin and the glass transition point of the amorphous resin.

In addition, in the toner production using a melt-kneading method, it is also effective to subject the melt-kneaded product obtained after the melt-kneading step to an annealing treatment in which the product is held at a temperature at least 5° C. higher than the melting point Tc of the crystalline resin for 30 minutes or longer in order to control (log G′(T1))/dT to be within the above range.

The means for making d(log G′(T1+3))/dT≤0 is not particularly limited because the storage elastic modulus of a general toner decreases as the temperature increases.

As a method of controlling the value of d(log G′(T1+3))/dT−d(log G′(T1))/dT to be within the above range, in the toner production by the melt-kneading method described above, it is effective to subject the melt-kneaded product obtained after the melt-kneading step to an annealing step in which the product is held at a temperature at least 5° C. higher than the melting point Tc of the crystalline resin for 30 minutes or longer. According to this step, eutectic formation of the crystalline resin and the wax proceeds to form a continuous layer, and the crystalline resin that has not formed a eutectic can independently form a discontinuous phase.

The toner has a G′(T1) of 5.0×10to 2.0×10Pa. G′(T1) is the value of G′(T) when the temperature T is T1. When G′(T1) is less than 5.0×10Pa, the scratch resistance of the fixed image decreases. On the other hand, when G′(T1) exceeds 2.0×10Pa, the low-temperature fixability decreases. G′(T1) is preferably 5.0×10to 2.0×10Pa, and more preferably 1.0×10to 1.0×10Pa.

The storage elastic modulus G′(T1) can be controlled, for example, by the following method.

For example, the storage elastic modulus can also be controlled by the amorphous monomer unit of the crystalline resin in addition to the amount of the crystalline resin added and the amount of the crystalline component in the crystalline resin. In addition, it can also be controlled by incorporating the amorphous resin into the toner particle or changing the type and content of the amorphous resin. In addition, it can also be controlled by incorporating a filler material into the toner particle. Specifically, G′(T1) can be easily increased by decreasing the amount of the crystalline resin added, decreasing the amount of the crystalline component in the crystalline resin, or increasing the filler content in the toner particle. In addition, G′(T1) can be easily decreased by increasing the amount of the crystalline resin added, increasing the amount of the crystalline component in the crystalline resin, or decreasing the filler content in the toner particle.

In addition, the toner has a G′(T1+30) of 1.0×10to 5.0×10Pa. G′(T1+30) is the storage elastic modulus at a temperature about 30° C. higher than the melting temperature of the crystalline resin, and corresponds to the storage elastic modulus of the toner in the fixing nip. That is, G′(T1+30) is the value of G′(T) when the temperature T is T1+30° C.

When G′(T1+30) is less than 1.0×10Pa, since the viscosity at the fixing nip part is too low, in fixing media with significant unevenness such as rough paper, the toner on the protruded portion melts and tends to flow into the depressed portion, and image density non-uniformity reflecting the unevenness of the fixing media, known as mottle, tends to occur. On the other hand, when G′(T1+30) exceeds 5.0×10Pa, the toner is unlikely to melt and the image glossiness decreases.

G′(T1+30) is preferably 5.0×10Pa to 3.0×10Pa, and more preferably 1.0×10Pa to 3.0×10Pa.